Conventionally, a method for fixing permanent magnets to a laminated core by resin sealing, such as one disclosed in Japanese Patent Application Gazette No. 2002-34187, has been known. The invention disclosed in the Gazette is constructed as follows. That is, core pieces blanked out by a pressing machine to have prescribed shapes are laminated and caulked, thereby forming a laminated core having a plurality of magnet insertion holes and resin injection holes located closer to an axis of the laminated core than the magnet insertion holes, both of the holes penetrating in the axial direction through the laminated core and being in communication with each other via communicating grooves. The laminated core thus formed is placed on a lower die and a permanent magnet is inserted in each of the magnet insertion holes. Subsequently, an upper die having inlets matching the respective resin injection holes and a resin supply hole communicated with the respective inlets is disposed above the laminated core. While the laminated core is pressed by application of a prescribed pressure on the upper die, resin material is injected into the resin injection holes of the laminated core from the inlets of the upper die. The resin material ejected from the resin injection holes is filled in the magnet insertion holes via the communicating grooves, and the resin is cured when heated under this condition, thereby fixing the respective permanent magnets in the magnet insertion holes of the laminated core.
The conventional method of resin sealing permanent magnets, however, has the following problems to be solved.
In filling the magnet insertion holes of the laminated core with the resin material, the resin material is injected into the magnet insertion holes through the resin supply hole and the inlets diverging from the resin supply hole formed in the upper die, and subsequently, through the resin injection holes and the communicating grooves of the laminated core. Accordingly, passages of the resin material become long. The long passages of the resin material require a great amount of resin and make it difficult to evenly fill the respective magnet insertion holes with the resin, which causes deterioration in reliability. Furthermore, because of the long passages of the resin, a pump for supplying the resin material is required to have a large supply pressure, and thus equipment becomes expensive.
Furthermore, in the technique disclosed in the above Gazette, the laminated core is fitted in a recess on the lower die and removed from the recess after heating. Such operation requires much time by either manual or mechanical means, and is extremely poor in workability.
The present invention has been made in view of the above situations and aims to provide a method of resin sealing permanent magnets in a laminated rotor core, which excels in productivity and workability and is capable of producing highly reliable products at low cost.